Patent application title: COMPOSITION COMPRISING A CONDUCTIVE POLYMER IN COLLOIDAL FORM AND CARBON

Abstract:

The present invention relates to compositions capable of forming a coating
and comprising a mixture of a conductive polymer in colloidal form and
carbon, methods for their manufacture and use for high-capacity
electrical double layer capacitors to be utilized in various electronic
apparatuses, power supplies and the like.

Claims:

1. A composition capable of forming a coating and comprising a mixture of
a conductive polymer in colloidal form, carbon black and a liquid
dispersion medium.

2. The composition according to claim 1, wherein the conductive polymer is
selected from the group consisting of polymers of anilines, thiophenes,
pyrroles and substituted derivatives thereof.

3. The composition according to claim 1, wherein two or more different
conductive polymers are present.

4. The composition according to claim 1, wherein the carbon black has a
specific surface area of more than 100 m2/g, as measured according
to the BET method.

5. The composition according to claim 1, wherein the carbon black is
active carbon black.

6. The composition according to claim 5, wherein the active carbon black
has a specific surface of greater than 750 m2/g.

7. The composition according to claim 1, wherein the average particle size
(number average) of the conductive polymer is smaller than 500 nm.

8. The composition according to claim 1, wherein the conductivity of the
conductive polymer is greater than 10.sup.-5 S/cm.

9. The composition according to claim 8, wherein the conductivity is
greater than 10 S/cm.

10. The composition according to claim 9, wherein the conductivity is
greater than 100 S/cm.

11. The composition according to claim 1, wherein the weight ratio of the
conductive polymer to carbon black is in the range of from 1:50 to 50:1.

12. The composition according to claim 1, comprising the liquid dispersion
medium in a concentration of from 40 to 99.5 weight percent, wherein the
dispersion medium liquid is evaporable under ambient conditions, and
further comprising other non-evaporable additives in a concentration of
from 0 to 10 weight percent, the conductive polymer and carbon components
being present in a concentration of from 0.5 to 60 weight percent, all
weight percentages being based on the total composition.

14. A method for manufacture of a composition according to claim 1,
comprising dispersing the conductive polymer and carbon black, and
optionally additives in a liquid dispersion medium and optionally drying
the liquid dispersion after application on a substrate.

15. The method of claim 14, wherein the conductive polymer is dispersed in
a first liquid and the carbon black is dispersed separately in a second
liquid, said liquids being the same or different, and the respective
dispersions are subsequently mixed together, optional additives being
added before, during or after the separate dispersion steps.

16. The method of claim 14, wherein the conductive polymer is dispersed in
a liquid and the carbon black is separately milled in the absence of
liquid, and wherein the dry milled carbon is subsequently added to the
liquid colloidal dispersion of the conductive polymer and dispersed
therein.

17. A composite material comprising the composition of claim 1 in the form
of a coating on a substrate.

18. The composite material of claim 17, wherein the substrate is selected
from the group consisting of metals, semiconductors, plastics, ceramics
and wood products.

19. An electrical or electronic article comprising the composition
according to claim 1.

20. The article of claim 19, wherein the article is selected from the
group consisting of conductors, energy stores, sensors, switches,
condensers, capacitors and supercapacitors, double layer capacitors and
redox capacitors.

21. A capacitor comprising an electrolyte and a pair of electrodes with a
separator disposed therebetween, wherein at least one of the electrodes
comprises the composition according to claim 1.

22. The capacitor of claim 21, wherein both electrodes comprise the
composition according to claim 1.

23. The capacitor of claim 21, wherein one electrode comprises the
composition according to claim 1 and the other electrode is a
conventional capacitor electrode.

24. The capacitor of claim 23, wherein the other electrode comprises a
current collector coated with a composition containing an intrinsically
conductive polymer but no carbon.

25. A composite material comprising the composition obtained by the method
of claim 14 in the form of a coating on a substrate.

26 The composite material of claim 25, wherein the substrate is selected
from the group consisting of metals, semiconductors, plastics, ceramics
and wood products.

27. An electrical or electronic article comprising the composite material
according to claim 25.

28. The article of claim 27, wherein the article is selected from the
group consisting of conductors, energy stores, sensors, switches,
condensers, capacitors and supercapacitors, double layer capacitors and
redox capacitors.

29. A capacitor comprising an electrolyte and a pair of electrodes with a
separator disposed therebetween, wherein at least one of the electrodes
comprises the composite material according to claim 25.

30. The capacitor of claim 29, wherein both electrodes comprise the
composite material according to claim 25.

31. The capacitor of claim 30, wherein one electrode comprises the
composite material according to claim 25 and the other electrode is a
conventional capacitor electrode.

32. The capacitor of claim 31, wherein the other electrode comprises a
current collector coated with a composition containing an intrinsically
conductive polymer but no carbon.

33. An electrical or electronic article comprising the composite material
according to claim 17.

34. The article of claim 33, wherein the article is selected from the
group consisting of conductors, energy stores, sensors, switches,
condensers, capacitors and supercapacitors, double layer capacitors and
redox capacitors.

35. A capacitor comprising an electrolyte and a pair of electrodes with a
separator disposed therebetween, wherein at least one of the electrodes
comprises the composite material according to claim 17.

36. The capacitor of claim 35, wherein both electrodes comprise the
composite material according to claim 17.

37. The capacitor of claim 35, wherein one electrode comprises the
composite material according to claim 17 and the other electrode is a
conventional capacitor electrode.

38. The capacitor of claim 37, wherein the other electrode comprises a
current collector coated with a composition containing an intrinsically
conductive polymer but no carbon.

Description:

TECHNICAL FIELD TO WHICH THE INVENTION PERTAINS

[0001]The present invention relates to conductive materials comprising
(intrinsically) conductive polymers and carbon materials, methods for
their manufacture and use for high-capacity electrical double layer
capacitors to be utilized in various electronic apparatuses, power
supplies and the like.

PRIOR ART

[0002]Conductive Materials are known and used in many different forms and
applications. Conductive materials based on carbon are available in
several different physical and chemical morphologies, forms and
compositions. Pure or mainly pure carbon is available in the form of
carbon black (which contains also mainly oxygen based impurities,
graphite (pure C), carbon nanotubes and fullerenes and the like. Another
group of conductive materials are (intrinsically) conductive polymers
which have found some first applications.

[0003]These two groups of conductive materials have at least one property
in common, the conductivity. Other properties may be exclusive to the one
or the other group of materials, or may vary widely within the respective
group. For example, the particle size of graphite is in the range of
several to several tens of microns, while that of fullerenes is in the
range of angstroms. The specific surfaces of carbon black and carbon
nanotubes exhibit high values up to about 1000 m2/g while that of
graphite is in the range of a few m2/g. Polyaniline, one of the
representatives of conductive polymers, is characterized by a rich redox
chemistry, PEDOT (polyethylenedioxythiophene), also termed PEDT, has a
moderately or poorly reproducible redox chemistry, while graphite or
carbon black show no reversible redox chemistry.

[0004]The combination of conductive polymers like polyaniline,
polyethylenedioxythiophene, polypyrroles or their derivatives with
carbonaceous materials (carbon black, graphite, carbon nanotubes and
fullerenes) has been tried in the past. While simple mixtures of said
materials do not offer any significant or reproducible advantage, and
hence did not find any commercial or technological applications, chemical
processes for the combination of conductive polymers and carbon black or
conductive polymers and carbon nanotubes have been widely studied. For
instance, the company Eeonyx has offered carbon black on which surface
polyaniline was polymerised as a developmental product in the market
("Eeonomer"), cf. G. Du, A. Epstein, K. Reimer, presentation on the March
1996 Meeting of the American Physical Society, Session M23, presentation
M 23.09. The laboratory chemicals supplier Aldrich has advertised such a
chemically produced mixture in their catalogue. However, such a product
did not offer interesting advantages.

[0005]One of the areas in which carbon black/polyaniline mixtures could
offer an interesting technological advantage, could be the area of so the
called `supercapacitors`, also often called `double layer` or `redox
capacitors`. This area provides the highest number of publications in
which carbon and conductive polymers have been mixed or provided in form
of a mixture.

[0006]For this purpose, principally two mixing procedures have been used:
[0007]Simple mixing of powders of carbon black and polyaniline by one day
of ball milling (US-Patent Application Publication No. 2002/0114128), or
in other ways as disclosed in Journal of Power Sources 11, 2003, 185-190,
and Journal of the Electrochemical Society, 148, 10, 2001, A1130-A1134,
where a polyaniline or polythiophene derivative was mixed with carbon
black powders. However, the specific means of mixing are not disclosed.
[0008]Chemical or electrochemical polymerisation of different conductive
polymers on the carbon black surface.

[0009]The latter method has been widely investigated in the patent and
scientific literature. European Patent Application EP 1 329 918 reports
about a negative electrode composite of carbon and polyaniline or
polypyrrole in which the conductive polymer was electrochemically
polymerised. The positive electrode was made from lead. The conductive
polymer content was found to be optimal at 10-15% by weight. The
capacitor made by using this material comprised an electrode combination
including a positive non-polarisable and a negative polarizable electrode
where the positive non-polarisable electrode was made from lead.

[0010]US Patent Application 2002/0089807 discloses an intrinsically
conductive polymer directly polymerised on highly porous carbon black
material by chemical or electrochemical means. The electrochemical
polymerisation of polyaniline on a carbon aerogel generated from
polyacrylonitrile is disclosed in Journal of Applied Electrochemistry 33,
465-473, 2003. That process is comparable to the electrochemical
polymerisation of polyaniline on active porous carbon disclosed in
Journal of Power Sources 117, 273-282, 2003 and lit. 10, Carbon 41,
2865-2871, 2003. In Conference Proceedings of ANTEC '98, Vol. 2, 1197ff,
1998, the authors report the polymerisation of polyethylenedioxythiophene
on high surface area films of carbon on a platinum current collector
support. In the same publication it was reported that polyaniline was
cast from hexafluoro-isopropanol solutions on the same type of carbon
films.

[0011]Electrochimica Acta Vol. 41, No. 1, 21-26, 1996 discloses various
redox supercapacitors in symmetry or non-symmetric electrode
configuration form in which various conductive polymers like polypyrrole
or polythiophene derivatives have been used and polymerised on the
substrate, in a comparable procedure as used in U.S. Pat. No. 5,527,640,
1996, where polythiophene derivatives were polymerised on carbon
substrates by electrochemical means.

[0012]As explained above, carbon black/conductive polymer mixtures have
often been prepared for use in so-called "supercapacitors". Such
capacitors are also often referred to as "double layer capacitors",
"electrochemical" or "electrical double layer capacitors" or "redox
capacitors" as well as sometimes "pseudo-capacity capacitors".

[0013]Conventionally, a double layer capacitor is an energy device in
which two electrodes--at least one of which being obtained by coating a
collector plate with a porous carbonaceous material having a high
specific surface area between and above about 100 and 1000 m2/g to a
collector plate--are disposed opposite to each other with a separator
disposed therebetween. A voltage is impressed on the electrodes in the
presence of an electrolyte solution, to generate an electrical double
layer on at least one of the electrodes, and energy can be taken out
therefrom. The structure of one kind of double layer capacitor using
porous carbonaceous material as electrode material is, as disclosed in
the specification and drawings of U.S. Pat. No. 5,150,283, classified
into a type in which a pair of electrical double layer electrodes (each
comprising a polarizable electrode joined to a collector plate) are wound
and contained in a container, and a button type in which a pair of
electrical double layer electrodes are laminated.

[0014]The wound type has a configuration in which a lead wire for giving
off energy to the exterior is attached to a collector plate composed, for
example, of an etched aluminum foil with a thickness of 20 to 50 μm.
The aluminum foil is coated with a paste composed of a powdered mixture
prepared by admixing an active carbon powder with a desired binder and a
desired conductive agent to form a conductive layer. A polarizable
electrode composed of an active carbon layer consisting mainly of active
carbon is formed on the conductive layer to obtain an electrical double
layer electrode, and a pair of such electrical double layer electrodes is
disposed opposite to each other with a separator disposed therebetween
and is wound.

[0015]Alternatively, the electrical double layer electrodes are assembled
by a method in which the polarizable electrode composed of the active
carbon layers and the separator are sufficiently impregnated with an
electrolytic solution containing an electrolyte dissolved therein under
vacuum. The electrodes and the separator are inserted into a case made of
aluminum or the like, and an opening portion of the aluminum case is
sealed by use of a packing. Generally, this assembly is of a cylinder
type.

[0016]On the other hand, the button type has a structure in which a
polarizable electrode composed of an active carbon layer is formed on a
disk-shaped sheet of a valve metal to obtain an electrical double layer
electrode. A pair of such electrical double layer electrodes is disposed
opposite to each other with an insulating separator therebetween, and
this assembly is housed in a metallic container composed of two members.
The two electrical double layer electrodes have their disk-shaped form
sheets (or foils) of valve metal joined respectively to the inner sides
of a bottom portion and a top cover portion of the metallic container,
the bottom portion and the top cover portion are joined to each other
while being hermetically sealed with an insulating ring packing at a
circumferential edge portion thereof, and the inside of the container is
filled with a nonaqueous electrolytic solution which is supplied
sufficiently to the electrical double layer electrodes and the separator.
As the nonaqueous electrolytic solution, for example, a solution prepared
by adding tetraethylammonium tetrafluoroborate to propylene carbonate is
utilized.

[0017]There are several other configurations of double layer capacitors or
redox capacitors (often called "supercapacitors") in use which will not
be described here in detail.

[0018]There has been proposed a high-capacity electrochemical capacitor in
which electrochemically active inorganic substances or organic
(intrinsically) conductive polymers are used as electrode materials in
combination with or in place of the above-mentioned porous carbonaceous
material and in which electric power storage based on the formation of
electrical double layers is utilized, in the same manner as in the
ordinary electrical double layer capacitor using the above-mentioned
porous carbonaceous material, and, simultaneously, electric power storage
based on an oxidation-reduction potential attendant on
oxidation-reduction reactions at both electrodes is utilized, to thereby
achieve a high capacity.

[0019]For example, an electrochemical capacitor using ruthenium oxide as
an electrode active substance (Physics Letters, 26A, p. 209 (1968)) is
evaluated to be the highest in performance of the electrochemical
capacitors using an inorganic oxide known at present, and has been
confirmed to have an energy density of 8.3 Wh/kg and an output density of
30 kW/kg.

[0021]Also, electrochemical capacitors using as electrode material
(intrinsically) conductive polymers utilizing the oxidation-reduction
characteristic of a π-conjugated system organic substance, other than
the above-mentioned inorganic metal oxides, have been actively studied in
recent years.

[0022]The electrochemical capacitors using the conductive polymers have
been investigated in many research institutes, and, as to the
characteristics, it has been reported that, for example, the use of
polypyrrole as electrode material gives a capacity of 86 C/g and an
energy density of 11 Wh/kg, the use of a mixture of polypyrrole and
polythiophene gives a capacity of 120 C/g and an energy density of 27
Wh/kg, and the use of poly-3-(4-fluorophenyl)thiophene gives a capacity
of 52 C/g and an energy density of 39 Wh/kg (J. Power Sources, vol. 47,
p. 89 (1994)).

[0023]Other than the above, in the type of utilizing intercalation for a
high-capacity capacitor, generally, a layer structure substance
(TiS2, MoS2, CoO2, V6O.sub.13) is used as the
electrode material. In this case, the device is in many cases assembled
with asymmetric electrodes (Japanese Translations of PCT for Patent Nos.
2002-525864, 2002-542582).

[0024]Furthermore, composite materials prepared from the above-mentioned
various electrode materials have been evaluated in some cases, to achieve
much higher capacities, as compared to the conventional capacitors using
only the porous carbonaceous material as an electrode material.

Problems to be Solved by the Invention

[0025]In spite of intensive research, no mixtures of carbonaceous
materials and (intrinsically) conductive polymers are in industrial use.
The reasons for this can mainly be found in a poor homogeneity of the
mixture on the nanoscopic scale and a poor reproducibility of the
properties due to the manufacturing processes (as described above) used.

[0026]On the other hand, the above-mentioned conventional electrical
double layer capacitors using a porous carbonaceous material for
polarizable electrodes are limited in capacity, though they are good in
quick charge-discharge characteristics. For example, as described in
Japanese Patent Laid-open No. 2003-338437, a capacitor using active
carbon (surface area: 650 m2/g) obtained by activation of a porous
carbonaceous material has an electrostatic capacity of 18.3 F/g, which is
lower than those of electrochemical capacitors.

[0027]As for the relationship between the electrostatic capacity and the
specific surface area of the porous carbonaceous material, an
electrostatic capacity of about 22 F/cc is obtained when the specific
surface area is in the range of 1500 to 2600 m2/g, but, when the
specific surface area is more than the range, the capacity is not
increased any longer but tends to the decreased ("Electrical Double Layer
Capacitors and Electric Power Storage Systems", The Nikkan Kogyo Shimbun,
Ltd., p. 9).

[0028]Other than the above, further examples of an electrode material
using a porous carbonaceous material are disclosed in Japanese Patent
Laid-open Nos. 2003-217982, 2003-81624, 2002-373835, and the like, but
each of the examples gives a lower capacity, as compared to those of
electrochemical capacitors, which matters particularly in use for
automobiles and the like.

[0029]Besides, when using only the porous carbonaceous material for
electrodes, it is necessary to add acetylene black or the like to the
binder for the purpose of enhancing conductivity, but, even with such an
addition, the interface resistance is very high, which constitutes a
serious problem.

[0030]On the other hand, there are electrochemical capacitors using a
conductive metal oxide as described above. Although such electrochemical
capacitors have very high capacities as compared to the cases of using
the above-mentioned porous carbonaceous material, the electrochemical
capacitors are disadvantageous on the basis of production cost, since the
metal of the metal oxide generally belongs to noble metals. For example,
pseudo-capacity capacitors using a thin film of ruthenium oxide or indium
oxide as electrode material have been reported to have an electrostatic
capacity of 160 F/cc in an aqueous system, in the 5th International
Seminar on Double Layer Capacitors and Similar Energy Storage Device held
in Florida, USA, in 1995.

[0031]Besides, the electrochemical capacitors using a conductive polymer
material as electrode material generally show a much higher capacity, as
compared with those of capacitors using the above-mentioned porous
carbonaceous material, but their characteristics may vary depending on
the method of forming the electrodes. For example, where the conductive
polymer is deposited on collector plates by an electrolytic
polymerization method as described in Japanese Patent Laid-open Nos. Hei
6-104141 and Hei 6-104142, the capacitor has a capacity of 3.7 F and an
internal resistance of 13.9 Ω, and the formation of electrodes by
the electrolytic polymerization method generally involves a serious
problem as to productivity thereof.

[0032]Therefore, many proposals have been made to use combinations of
carbonaceous materials (mainly carbon black) and intrinsically conductive
polymers. As described above, only two methods have been used to prepare
such mixtures--a dry blending method of powders (by ball milling and the
like) and the polymerisation of the conductive polymer in presence of the
carbon black.

[0033]The method of synthesizing a conductive polymer by chemical
oxidation polymerization and preparing a composite material from the
conductive polymer and other conductive inorganic material is an
apparently relatively simple technology for forming electrodes, and many
examples of this technology have been made publicly available in recent
years. However, its reproducibility is poor and therefore, no such
mixtures are in practical use. Also, the problems to be overcome when
trying to scale up and develop a reproducible process are huge.

[0034]For example, Japanese Patent Laid-open No. 2002-265598 discloses the
use of a composite material of an organic conductive oligomer and an
inorganic material as electrode material. In this case, however, the
organic conductive oligomer cannot be expected to have a high
conductivity, so that the inorganic material is required to have a very
high conductivity in order to lower the internal resistance.

[0035]Besides, as a similar case of using a conductive polymer material, a
method of polymerizing the conductive polymer in a porous carbonaceous
material (Japanese Patent Laid-open No. 2001-210557) cannot produce a
conductive polymer with a high conductivity but leads to an increase in
the internal resistance of the capacitor.

[0036]As has been described above, there have hitherto been known a large
number of examples of a capacitor using an electrochemically active
conductive polymer or inorganic oxide. However, the use of the inorganic
material leads to a problem as to production cost, whereas the use of the
conductive polymer involves difficulties in control of conductivity,
control of particle size and reproducibility, resulting in that the
capacitors cannot show sufficient performance.

[0037]It was therefore the object of this invention to create a carbon
material/conductive polymer mixture which can be manufactured in a
reproducible manner and shows superior performance values especially for
the manufacture of supercapacitors.

DETAILED DESCRIPTION OF THE INVENTION

[0038]Most surprisingly, a mixture of (intrinsically) conductive
polymer(s) with carbon materials like carbon black, graphite, carbon
nanotubes or fullerenes, can reproducibly be manufactured, if the
conductive polymer(s) is (are) provided in colloidal form and the
colloidal form of the conductive polymer is mixed with the carbon
material.

[0039]Thus, in a first aspect, the present invention relates to
composition capable of forming a coating and comprising a mixture of a
conductive polymer in colloidal form and carbon.

[0040]In a second aspect, the present invention relates to a method for
the manufacture of a composition according to the first aspect, said
method comprising dispersing the conductive polymer and carbon, and
optionally additives in a liquid dispersion medium and optionally drying
the liquid dispersion after application on a substrate.

[0041]In a third aspect, the present invention relates to a composite
material comprising the composition according to the first aspect or the
composition obtained by the method of the second aspect in the form of a
coating on a substrate.

[0042]In a fourth aspect, the present invention relates to an electrical
or electronic article comprising the composition according to the first
aspect or the composite material according to the third aspect.

[0043]Preferred embodiments of the present invention are disclosed in the
dependent claims.

[0044]Preferably, the carbon materials of the present invention are
selected from the group consisting of graphite, carbon black, nanotubes
and fullerenes. The carbon materials of the present invention are also
referred to as `carbon-based materials` since they do not necessarily
consist exclusively of the chemical element carbon but may also comprise
other elements such as hydrogen, oxygen, nitrogen and sulphur. For
example, carbon black may contain 0.3-1.3% H, 0.1-0.7% N, and 0-0.7% S.
Depending on the mode of manufacture, the oxygen content of carbon black
may amount to 0-1.5% for furnace and thermal type carbon blacks, up to 5%
for gas and channel type carbon blacks, and up to 15% for carbon black
post-treated with oxygen. Further, condensed aromatics may be present at
the surfaces of the material.

[0045]The term "(intrinsically) conductive polymers" (ICP) refers to
organic polymers which have (poly)-conjugated π-electron systems (e.g.
double bonds, aromatic or heteroaromatic rings or triple bonds). They can
exist in various states, each described by different empirical formulae,
which can generally be converted essentially reversibly into one another
by (electro)chemical reactions such as oxidation, reduction, acid/alkali
reaction or complexing. These reactions are also occasionally known as
"doping" or "compensation" in the literature, or can be regarded as
"charging" and "discharging" in analogy with the electrochemical
processes in batteries. At least one of the possible states is a very
good conductor of electricity, e.g. has a conductivity of more than 1
S/cm (in pure form), so one can speak of intrinsically conductive
polymers. These forms of the ICP are generally regarded, as poly-radical
cationic or anionic salts. A good overview of the (intrinsically)
conductive polymers synthesised to date with a chemical structure
suitable for the present objective, can be found in Synthetic Metals,
Issues 17, 18 and 19 (1987), and in Synthetic Metals (in press),
Proceedings of the ICSM '88 (Santa Fe).

[0046]The chemical nature of the conductive polymers of the invention is
not particularly limited, and examples thereof include polyaniline,
polyaniline derivatives, polythiophene, polythiophene derivatives,
polypyrrole, polypyrrole derivatives, polythianaphthene,
polythianaphthane derivatives, polyparaphenylene, polyparaphenylene
derivatives, polyacetylene, polyacetylene derivatives, polydiacethylene,
polydiacetylene derivatives, polyparaphenylenevinylene,
polyparaphenylenevinylene derivatives, polynaphthalene, and
polynaphthalene derivatives, polyisothianaphthene (PITN),
polyheteroarylenvinylene (ParV), in which the heteroarylene group can be
e.g. thiophene, furan or pyrrol, polyphenylene-sulphide (PPS),
polyperinaphthalene (PPN), polyphthalocyanine (PPhc) etc., and their
derivatives (formed for example from monomers substituted with side
chains or groups), their copolymers and their physical compounds. The
method for polymerizing the conductive polymers is not particularly
limited, and the usable methods include electrolytic oxidation
polymerization, chemical oxidation polymerization, and catalytic
polymerization. The polymer obtained by the polymerizing method as
mentioned is neutral and is not conductive per se. Therefore, the polymer
is subjected to p-doping or n-doping to be transformed into a conductive
polymer. The substance used for the doping is not particularly limited;
generally, a substance capable of accepting an electron pair, such as a
Lewis acid, is used. Examples include hydrochloric acid, sulfuric acid,
organic sulfonic acid derivatives such as parasulfonic acid,
polystyrenesulfonic acid, alkylbenzenesulfonic acid, camphorsulfonic
acid, alkylsulfonic acid, sulfosalycilic acid, etc., ferric chloride,
copper chloride, and iron sulfate.

[0047]It is not critical in the practice of the present invention in which
form the carbon based material is provided. The colloidal form of the
conductive polymer can be mixed with the carbon based material provided
in (dry or wet) powder form, in form of a porous film or composite or
also in form of a colloidal formulation. The carbon can be pretreated
(e.g. by ball milling), predispersed in water, organic solvent or another
medium or shaped in form of fibres, nanofibres, films or porous shapes or
membranes. The colloidal form of the conductive polymer may be added to
the carbon based material or vice versa.

[0048]For instance, the carbon powder can be added to a colloidal
dispersion of the conductive polymer. Alternatively, the conductive
polymer dispersion can be added to the carbon by coating a carbon
substrate with the colloidal dispersion of the conductive polymer.

[0049]The colloidal form of the conductive polymer can be manufactured in
various different ways which are basically known and state of the art.
See for example EP-A-0 329 768 and German patent application No. 10 2004
003 784. According to the present invention, polymer particles having a
size of smaller than 500 mm are considered to be colloidal. The size of
the particles can be determined by scanning or transmission electron
microscopy, or by using laser Doppler technology. Another method of
manufacture of the polymer is its polymerisation in the presence of
surface active agents so that the resulting polymer remains in colloidal
form in the reaction medium. For the subsequent use as colloidal
dispersion, one would purify the dispersion by ion exchange and/or
membrane filtration.

[0050]Alternative methods are procedures by which the conductive polymer
is polymerised, then neutralised (compensated) to the non-conductive form
and mixed with solvents resulting in a fine colloidal dispersion (often
considered to be a "solution"). This colloidal dispersion of the
non-conductive form of the conductive polymer can be mixed with the
carbon based material and the resulting mixture can be rendered
conductive by adding appropriate materials ("dopants") like Broenstedt
acids, Lewis acids or oxidants (like iodine, FeCl3 or else).

[0051]Another preferred way is to polymerise the conductive polymer so
that it precipitates from the reaction medium, can be filtered, washed
and afterwards dispersed. This manner of polymerisation is described in
EP-B-0 329 768. Polymers obtained by that process are commercially
available from Ormecon GmbH, Germany. See in particular Example 1 and the
description at page 8, lines 7-22 of EP-B-0 329 768.

[0052]The most preferred way is to use conductive polymer dispersions
manufactured as described in German patent application No. 10 2004 003
784, filed Jan. 23, 2004. See in particular claim 6 and Examples 1 to 8
therein. The process of German patent application No. 10 2004 003 784
allows one to prepare colloidal conductive polymers having a conductivity
of above 100 S/cm which is advantageous for many applications. In the
process, the conductive polymer is in general first polymerised according
to the polymerization method of EP-B-0 329 768 so that the primary
particles have a diameter of less than 500 nm, and the resulting powder
is dispersible. According to one embodiment, this powder is then
dispersed in a first dispersion step, followed by a conditioning step and
a second dispersion step. Finally, the dispersion is formulated so that
the colloidal dispersion meets the various following processing and
applications requirements (viscosity, stability, drying time and
temperature, and others). Suitable dispersion techniques are described in
German patent application No. 10 2004 003 784 and include, for example,
the use of an ordinary ball mill, a planetary ball mill, a homogenizer,
or an ultrasonic dispersing apparatus.

[0053]The conductive polymer can be mixed with the carbon based material
after the second dispersion step (which usually results in a highly
viscous paste form) or after the final formulation step (which usually
results in a less viscous liquid).

[0054]The carbon based materials preferably used for this invention are
carbon nanotubes, nanofibres, fullerenes, carbon black and the like.
These materials tend to agglomerate and are usually not easily
impregnated with liquids or colloidal dispersions.

[0055]Because it is advantageous for the later use of the
carbon/conductive polymer mixtures, the surface of the carbon based
materials should be accessible for the colloidal conductive polymer.
Therefore it is preferred to provide the carbon based material in form of
highly porous structures, fine powders or colloidal dispersions. If dry
powders are used, it is preferred to pretreat these powders, e.g. by ball
milling. Ball milling can be carried out in planetary mills or satellite
ball mills.

[0056]The carbon based materials can also be dispersed in presence of the
colloidal dispersion of the conductive polymer, e.g. in ball mills.

[0057]It is also preferred to manufacture a dispersion of the carbon based
material in water or organic solvents (with or without using surface
active agents, tensides and other materials). Such a dispersion can be
made in ball mills, pearl mills, ultrasonic dispersion apparatuses, 2- or
3-roll mills or other state-of-the-art dispersion machines.

[0058]In order to attain a highly dispersed state, the dispersing process
can be carried out by use of an ordinary ball mill, a planetary ball
mill, a homogenizer, or an ultrasonic dispersing apparatus. Where the
planetary ball mill is used, stirring is preferably carried out for at
least 30 min. Stirring for a long time may be associated with processing
problems such as a rise in the temperature of the solvent. Therefore,
cooling is needed in the case of stirring for more than 1 hour.

[0059]It is preferred to produce a paste of the carbon based material
which can be mixed with the conductive polymer colloid without, before,
during or after further dilution and formulation.

[0060]The relation between carbon and conductive polymer may widely vary.
For example, the weight ratio of the conductive polymer to carbon may
range from 1:50 to 50:1 or 1:50 to 50:2.

[0061]The final mixture of carbon and conductive polymer may contain
additives like surface active agents or stabilisers, and other materials.

[0062]The selection of the carbon based material to be combined with the
colloidal conductive polymer is only limited by availability, price and
suitability for the final application. Mixtures of different carbon based
materials, like active carbon black and conductive carbon black may be
advantageous in certain applications.

[0063]The same applies to the conductive polymer. Although it is not
critical to the process or application requirements of this invention,
availability and price may limit the selection of conductive polymers.
Generally, all of the above described conductive polymers are useful in
the practice of the present invention. Preferred are polyanilines and
polythiophenes and their derivatives, in particular polyaniline and its
copolymers and derivatives.

[0064]Carbon/conductive polymers according to this invention can be used
in conductors, energy stores, sensors, switches, condensers, capacitors
and supercapacitors, double layer capacitors and redox capacitors

[0065]For the application of carbon/conductive polymers according to this
invention for the storage of (electrical) energy, e.g. in capacitors,
active carbon black and polyanilines or polythiophenes and their
derivatives are preferred. Conductive carbon black may be used as an
additional component as well.

[0066]A preferred application of the compositions according to the
invention is their use as electrode material in high-capacity capacitors.
Such capacitors are often called "super-capacitors" or "double layer
capacitor" ("DLC"), also sometimes (referring to some specific mechanism
in certain forms of such capacitors) "redox capacitors". In the
following, this application will be referred to as "DLC".

[0067]One preferred embodiment of the invention is the manufacturing of
materials for electrodes for a high-capacity capacitor comprising a
porous carbonaceous material or a valve metal, at least one of the
electrodes being formed from a composition containing an
electrochemically active substance. Surprisingly, by combining the
carbonaceous material with the conductive polymer in colloidal form, it
is possible to strongly bind the porous carbonaceous material and to form
a stable electrode or electrodes. While in the prior art a non-conductive
organic binder has been used as a binder for binding the porous
carbonaceous material, the conductive material according to the invention
makes it possible to form the electrode without using a binder. In
addition, the adhesive force for adhesion to a collector plate can be
sufficiently secured by controlling the particle diameter. Moreover, the
performance data indicate the superior formation of an electrical double
layer, and the material according to the invention can easily impregnated
with the electrolyte solution.

[0068]Although it is not critical for the scope of this invention,
usually, for the use as electrode material, the mixture contains a higher
amount of (active) carbon than conductive polymer.

[0069]The conductivity of the conductive polymer contributes particularly
to a reduction in the equivalent series resistance of the capacitors.
While it is a general practice to add acetylene black or the like as a
conductivity-imparting material in the case of an electrode for a
capacitor which uses a porous carbonaceous material, the material
according to the invention is characterized in that, by providing a
conductive polymer with conductivity of 100 S/cm or more, the conductive
polymer by itself has the function as a conductivity-imparting material,
making it unnecessary to especially add a conductivity-imparting
material. Since it is unnecessary to add a conductivity-imparting
material, it is possible to enlarge the capacity of the actual product.
In this case, the conductivity of the conductive polymer is at least 100
S/cm, preferably 200 S/cm or more, and more particularly 500 S/cm or
more. The conductivity is preferably as high as possible, since it has a
great influence on the internal resistance of the capacitor to be made.

[0070]In a further embodiment of the invention, the conductive polymer is
dispersed in water or an organic solvent. Particularly, the composition
specified conditionally can be used separately for the case where the
electrolyte in the capacitor is water and for the case where the
electrolyte is an organic solvent. Especially where the electrolytic
liquid is water, the use of the conductive polymer dispersed in an
organic solvent is advantageous to the stability of the electrode.

[0071]In another embodiment of the invention, an electrode composition for
a capacitor is provided, wherein the conductive polymer dispersion
element contains solid components in a concentration of not more than 20
wt %. Particularly at the time of forming the electrodes, the
concentration of the solid components greatly influences the productivity
and cost. However, the solid components in the conductive polymer
dispersion element influences the stability of the dispersion, too.
Therefore, the concentration of the solid components is not more than 20
wt % where production cost is taken into account, and the concentration
is not more than 10 wt %, preferably not more than 5 wt %, where the
stability of the dispersion is also taken into account.

[0072]In still another embodiment of the invention, it is preferred to
focus on the specific surface area of the porous carbonaceous material. A
sufficient capacity of the DLC can be obtained by use of a carbonaceous
material with a specific surface area of not less than 100 m2/g,
preferably 500 m2/g, more preferably 1000 m2/g. Such a porous
carbonaceous material is dispersed in the conductive polymer dispersion
element.

[0073]The amount of the porous carbonaceous material used can widely vary.
It is necessary to add the porous carbonaceous material in an amount of
at least 5 wt %, in relation to the weight of solid polyaniline.

[0074]The addition amount is closely related to the charge-discharge rate
of the capacitor. It is desirable to add the porous carbonaceous material
in a larger amount in the case of devices for quick charge-discharge, and
to add the conductive polymer in a larger amount in the case of devices
for slow charge-discharge. Thus, according to the present invention, it
suffices to control the addition amount according to the device
requirements. In order to obtain a capacitor with a capacity of at least
greater than that of a capacitor using solely the porous carbonaceous
material, it is necessary to add the conductive polymer in an amount in
terms of solid components of not less than 5 wt %. In order to obtain a
sufficient oxidation-reduction performance, it is necessary to add the
conductive polymer in an amount in terms of solid components of
preferably not less than 10 wt %.

[0075]In still another embodiment of the invention, the materials are used
for electrodes for a DLC, said electrodes being disposed opposite to each
other with the separator disposed therebetween, wherein both of the two
electrodes are composed of the same kind of conductive polymer. This
configuration has the merit of providing a very inexpensive device, in
consideration of the productivity thereof.

[0076]In still another embodiment of the invention, the materials are used
for electrodes for a DLC, wherein the compositions used to form the two
electrodes disposed opposite to each other with the separator disposed
therebetween comprise different kinds of conductive polymers. This is
based on the consideration that many of organic conductive polymers show
different activities under a positive voltage and under a negative
voltage. In other words, a method of obtaining a high-capacity device
resides in using a conductive polymer material which shows the highest
electrical activity when the voltage is swept.

[0077]In still another embodiment of the invention, the materials are used
for electrodes for a DLC, wherein one of the two electrodes comprises a
porous carbonaceous material, and the other comprises a porous
carbonaceous material/conductive polymer composite according to the
invention. This configuration shows a surprisingly high capacity.

[0078]In still another embodiment of the invention, the materials are used
for electrodes for a DLC, wherein one of the two electrodes comprises a
metal oxide, and the comprises a porous carbonaceous material/conductive
polymer mixture according to the invention. This configuration is
effective particularly in the case of obtaining a high capacity by
utilizing the oxidation-reduction characteristics of the metal oxide
electrode. Particularly desirable examples of the material of the metal
oxide electrode are ruthenium oxide and indium oxide.

[0079]Moreover, where the inorganic material/conductive polymer composite
body in the present invention is formed into a film or other molded
product, it is possible to add a stabilizer, a light stabilizer, a
filler, a binder, a conductivity-imparting agent and the like, as
required.

[0080]The effects of using carbon/colloidal conductive polymer mixtures as
electrode materials in DLC are quite surprising. Compared with such types
of capacitors manufactured by polymerising a conductive polymer in
presence or on the surface of (active) carbon black used in DLC, the
capacitors manufactured using the mixtures according to this invention
exhibit significantly better properties. However, it is noted that the
scope of this invention is not limited by the specific properties of the
DLC manufactured according to the invention. In other words, DLCs which
may show a lower performance are also considered to be within the scope
of this invention.

[0081]The capacity may range from, for example, over 50 to well over 200
F/g, the power density may range, for example, from about 1,000 to
several 1,000 W/kg, and the energy density ranges, for example, from
about 10 and well over 100 Wh/kg.

[0082]As can be seen in FIG. 6 and FIG. 11 (Ragon plots), this set of
characteristics positions the DLC according to the invention outside of
the presently accessible range of power and energy density, significantly
higher than DLCs (supercapacitors) and even Lithium ion batteries of the
present state of the art.

[0083]Some of the reasons for this surprising effect may be--without
intending to be limited by this explanation--(a) that there is no need
any more for adhesive or film forming additives (in order to form an
adhering electrode material layer on the surface of the metallic
collector) (b) a lower internal resistance and (c) the additional
possibility of redox reactions, all together increasing the accessible
surface (accessible for charge carriers and their exchange), the wetting
of the electrolyte on the electrode material and the energy density
(charge per weight).

[0084]Pulverized coconut shell active carbon (not yet activated) in an
amount of 18 g was dispersed in 90.9 g of a conductive polymer dispersion
(ORMECON 7301-026-002, a dispersion of conductive polyaniline in xylene;
solid components: 2.2%), and the mixture was stirred by a planetary ball
mill for 60 min. To the porous carbonaceous material/conductive polymer
slurry, 57.3 g of xylene was further added, and the mixture was stirred
by a stirring motor for 30 min, to prepare a porous carbonaceous
material/conductive polymer dispersion.

[0085]Electrodes for a capacitor need collector plates adapted to the
electrolytic solution used in the capacitor. In this example, platinum
plates were used for electrodes when using aqueous sulfuric acid solution
(1 mol/l) as the electrolytic solution, and aluminum was used for the
electrodes when using propylene carbonate as the electrolytic solution.
Where platinum is used for the collector plates in the actual electrodes
for the capacitor, the surfaces of platinum plates are first scratched
with a file, and are then coated with a fixed amount of the porous
carbonaceous material/conductive polymer dispersion prepared as described
above. Then, the coated platinum plates are placed in a high-temperature
tank at 100° C. for 1 hour to sufficiently remove the organic
solvent. The electrodes thus formed were subjected to weighing of the
electrode active substance, and were used directly as the electrodes for
the capacitor.

[0086]When using a 1 mol/l solution of tetraethylammonium
tetrafluoroborate in propylene carbonate as an organic solvent based
electrolytic solution, aluminum plates were used as collector plates. The
aluminum collector plates were scratched by a file and coated with a
fixed amount of the porous carbonaceous material/conductive polymer
dispersion, in the same manner as in the case of using the platinum
plates as the collector plates. Thereafter, drying was conducted at
100° C. for 24 hours, to sufficiently remove moisture.

[0087]The components of the dispersion used for forming the porous
carbonaceous material/conductive polymer composite electrodes are shown
in the following Table 1.

[0088]Each electrode plate with the electrode active substance in close
contact therewith, as prepared in Example, 1 is blanked into circular
disks with a diameter of 1 cm, to prepare two electrodes. A glass fiber
filter is blanked into a circular shape with a diameter of 1.5 cm and
used as a separator. Further, an aqueous 1 M solution of sulfuric acid is
used as an electrolytic solution in the case of an aqueous system. A 1 M
solution of tetraethylammonium tetrafluoroborate in propylene carbonate
is used as an electrolytic solution in the case of an organic solvent
system.

Evaluation of Capacitor Characteristics

[0089]Measuring Instruments: The internal resistance of each capacitor
cell was measured by use of an impedance analyzer YHP 4192A, available,
from Hewlett-Packard Development Company, L.P. Measurements in a
charge-discharge test were carried out by use of a TOYO System
TOSCAT-3100U, available from TOYO SYSTEM, Co. LTD.

[0090]The results of the charge-discharge test of capacitors using the
electrode active substances shown in Experimental Example 1 are shown as
Examples in the following Table 2.

[0091]The results of evaluation of internal resistance are shown in FIG. 1
and FIG. 2. Measurement was conducted by use of a capacitor cell formed
by using the electrodes using the dispersion elements of Experiment 2 and
Experiment 5, and using a 1 M sulfuric acid solution as the electrolytic
solution.

[0092]FIG. 1 shows the internal resistance of the capacitor (impedance
characteristics) using the porous carbonaceous material with a specific
surface area of 1600 m2/g.

[0093]FIG. 2 shows the internal resistance of the capacitor (impedance
characteristics) using the porous carbonaceous material with a specific
surface area of 1100 m2/g.

Comparative Example

[0094]A mixture of an electrode material including 60 wt % activated
carbon (specific surface area of about 1600 cm2/g), 30 wt % carbon
black, and 10 wt % tetrafluoroethylene as binder was prepared. For film
formation methanol was added to this mixture. An electrode sheet (10 mm
width, 10 mm length, 3 mm thickness) was prepared by using a rolling
method. This sheet was dried at 250° C. at overwise ambient
conditions.

[0095]Charge-discharge test were then carried out using the same method as
described above in Example 2. In this case, the charge capacity was about
4.7 F/g only.

Example 3

1) Agent and Apparatus:

[0096]BELLFINE AP, which is produced by KABEBO LTD, was used as active
carbon material.

[0097]D1005W (dispersion of polyaniline in water) and 7201-026-001
(dispersion of polyaniline in xylene), both available from Ormecon GmbH,
Ammersbek, Germany were used as conductive polymers in colloidal form.

[0099]The mixture was prepared by using the following procedure. 8.0 g of
the active carbon and 90.9 g of ORMECON 7201-026-001 (solid: 2.20%) were
mixed using a Satellite ball mill for 60 min. This mixture was used as
electrode material. Electrode films were made by applying a 200 μm
coating of the material on an aluminum plate. The wet film was dried at
100° C. under ambient conditions.

[0100]Charge-discharge testing was carried out using the thin film having
a mixture of 7201-026-001 and BELLFINE AP. Charge-discharge properties
were determined at 0.5 mA/cm2, 1 mA/cm2, and 5 mA/cm2.
Initial capacities under these conditions are listed in Table 3.

[0101]Both power density and energy density were excellent. This capacity
is bigger than that of a capacitor made from BELLFINE carbon only. For
the `BELLFINE only` capacitor, the capacity is about only 30 F/g. Results
of cycle tests are indicated in FIG. 3, FIG. 4, and FIG. 5.

[0102]FIG. 3 shows the result of a cycle test of capacitor at a current
density of 0.5 mA and a voltage of 2.0V using a propylene carbonate
electrolyte including 0.01M tetraethylammonium tetrafluoroborate.

[0103]FIG. 4 shows the result of a cycle test of capacitor at a current
density of 1.0 mA and a voltage of 2.0V using a propylene carbonate
electrolyte including 0.01M tetraethylammonium tetrafluoroborate.

[0104]FIG. 5 shows the result of a cycle test of capacitor at a current
density 5.0 mA and a voltage of 2.0V using a propylene carbonate
electrolyte including 0.1M tetraethylammonium tetrafluoroborate

[0105]After the 4000 cycle test, the capacitance decreased to about 1/3 of
the initial value. Capacitance after 4000 cycles is listed in Table 4.

[0106]A Ragon-plot of this cycle test data is shown in FIG. 6. It can be
seen that the capacitance of the evaluated capacitor is higher than that
of conventional ones. Specifically, energy density decreases with an
increasing number of cycles. Clearly, however, power density hardly
changes as compared to the initial value. In the case of 5 mA/cm2
condition, the characteristic got worse quickly after about 4500 cycles.

[0107]In order to understand the resistance components, impedance
characteristics were measured. Measurement of impedance was carried out
in the range from 5 Hz to 13 MHz. The interface action of ion species,
however, cannot be seen in this frequency area. First, the resistance
component was checked by a Cole-Cole plot. Then change of each resistance
was conformed by comparing with the Cole-Cole plot of initial resistance
component with that of resistance component after 4000 cycles. In the
case of this capacitor, equivalent circuit was depicted as follow;

##STR00001##

[0108]In the case of a capacitor, R1 is a solution resistance which is in
series with electrode interfacial impedance, and R2 is the Faradaic
resistance of electrode process at reversible potential. This value is
influenced by the resistance of conducting polymer. The Cole-Cole plot is
shown in FIG. 7.

[0110]The above data shows that, although R1 did not change with both
current density, R2 changed drastically with 4000 cycles. It is assumed
that this change was dependent on the change of conductive polymer
resistance such as elimination of dopant, oxidation of conductive
polymer, decomposion of polymer and so on.

2. Water Dispersed Polyaniline (D1005W)

[0111]Charge-discharge test was carried out by the use of thin film on Al
plate, which was made from mixture of D1005W and BELLFINE AP.
Charge-discharge tests were performed at 0.5 mA/cm2, 1 mA/cm2,
and 5 mA/cm2. Initial capacities under these conditions are listed
in Table 6.

[0112]Energy density of capacitor using D1005W was less than that of
capacitor using 7201-026-001. Results of Cycle test are shown in FIG. 8,
FIG. 9, and FIG. 10.

[0113]FIG. 8 shows the result of a cycle test of capacitor at a current
density of 0.5 mA and a voltage of 2.0V and using a propylene carbonate
electrolyte including 0.01M tetraethylammonium tetrafluoroborate

[0114]FIG. 9 shows the result of a cycle test of capacitor at a current
density of 1.0 mA and a voltage of 2.0V and using a propylene carbonate
electrolyte including 0.01M tetraethylammonium tetrafluoroborate.

[0115]FIG. 10 shows the result of a cycle test of capacitor at a current
density of 5.0 mA and a voltage of 2.0V and using a propylene carbonate
electrolyte including 0.01M tetraethylammonium tetrafluoroborate.

[0116]In the case of 1.0 mA/cm2, change of capacitance was not observed in
the cycle test. In the case of 5.0 mA/cm2, however, a rapid reduction of
capacitance was observed at 1000 cycles. The capacity data after 4000
cycles are listed in Table 7.

[0118]From the data it is apparent that energy density decreases with an
increasing number of cycles. However, power density hardly changes as
compared to the initial value. At a current density of 1.0 mA/cm2,
power density and energy density were very stable for about 4000 cycles.
At 5.0 mA/cm2, power density got worse quickly after about 1000
cycles.

[0119]In order to analyse the resistance component, impedance measurements
was carried out using impedance analyzer. Results of the impedance
measurement are shown in FIG. 12, which is a Cole-Cole Plot of capacitor
using mixture of conductive polymer and active carbon as electrode.

[0121]This R2 resistance component is bigger than that of 7201-026-001
based capacitor's R2. Without being bound by theory, it is assumed that
the difference of R2 resistance between D1005W based capacitor and
7201-026-001 based capacitor can be attribute to difference of
conductivity between D1005W and 7201-026-001. Both of R1 and R2
resistance increased drastically after 4000 cycles.

Effects of the Invention

[0122]As has been described above, the present invention provides an
electrical double layer capacitor in which a pair of polarizable
electrodes each comprising a solid electrolyte of a conductive polymer
contained in an active carbon layer are opposed to each other with a
separator disposed therebetween. Particularly, by enhancing the particle
diameter and conductivity of the conductive polymer, it is possible to
obtain an electrical double layer capacitor having a low internal
resistance and a high capacity.